I wear a medium kuiu guide jacket so I ordered a medium Tiburon Zip T. Forearms were unbearably too tight. I reordered the Large. Forearms are still a bit tight, but thinking I wont have to wear a armguard??? I just thought I have lived all this life unknowingly with extremely large forearms. looks like its not just me :) Cant wait to try the shirt out in the Colorado high country this aug/sept.